The present invention pertains to tubes and, more particularly, to partially adhered tubes, and methods and apparatus for manufacturing them.
Tubes are often used as packages for containing products. For example, it is common to close the ends of tubes with caps to form containers for carrying products, such as food. Tubes are also commonly used as cores for having products, such as paper and textile goods, wound thereon. When tubes are used as cores, it is important that respective surfaces of the one or more plies of the tube be securely adhered to one another to ensure that the tubes can withstand the stresses that are incurred while products are wound onto, or unwound from, the tubes, and while the products are carried by the tubes. Accordingly, it is common for tubes used as cores to be “fully adhered”, as described below.
A composite tube, which can be used as a core, can be made by wrapping plies of paperboard around an axis of the tube, so that an outer surface of an inner ply confronts, and is adhered to, an inner surface of an outer ply. It is typical in many situations for at least about 95% to 100% of the outer surface of the inner ply to be adhered to the inner surface of the outer ply. Tubes with that level of adhesion are often referred to as “fully adhered”
FIGS. 1-6 respectively illustrate composite tubes and methods and apparatus for manufacturing them, in accordance with some of the known prior art. FIG. 1 illustrates a portion of an apparatus 20 for making composite tubes 22 that include four plies 26a-c. The apparatus 30 includes a mandrel 24 about which the plies 26a-c are spirally wrapped to form a tubular structure 28. The tubular structure 28 is cut into lengths to form the tubes 22. The mandrel 24 has a cross-sectional shape corresponding to the desired cross-sectional shape of the tubes 22.
More specifically, an innermost ply 26a is spirally wound onto the mandrel 24 into a tubular shape to partially form the tubular structure 28. Adhesive is applied to what will become the inner surface of an inner body ply 26b, and then the inner surface of the inner body ply is wound onto and adhered to the outer surface of the innermost ply 26a to further partially form the tubular structure 28. Adhesive is applied to what will become the inner surface of an outer body ply 26c, and then the inner surface of the outer body ply is wound onto and adhered to the outer surface of the inner body ply 26b to further partially form the tubular structure 28. Adhesive is applied to what will become the inner surface of an outermost ply 26d, and then the inner surface of the outermost ply is wound onto and adhered to the outer surface of the outer body ply 26c to further form the tubular structure 28.
The outer surface of the tubular structure 28 is engaged by a winding belt 30 that is wrapped about a pair of winding cylinders 32 such that the belt 30 spirally advances the tubular structure along the mandrel 24. Although only a single winding belt 30 is shown in FIG. 1, additional winding belts may be employed at different locations along the tubular structure 28. At a position downstream from the winding belt 30, the tubular structure 28 is cut to desired lengths at a cutting station, to form the shorter tubes 22.
As illustrated in FIG. 2, caps 36 can be applied to the ends of a tube 22 to form a can. One of the caps 36 is partially cut away in FIG. 2 to show the interior of the can, which is where products may be contained. In contrast to what is illustrated in FIG. 2, it is common for a can with end caps 36 to include only one of the body plies 26b or 26d. The ends of the tubes 22 typically are not closed with caps 36 if the tubes 22 are to function as cores around which products are wound.
The body plies 26b, 26c can be referred to as structural body plies because each is typically thicker and stronger than the innermost ply 26a and the outermost ply 26d, such that the body plies 26b, 26d are responsible for providing a majority of the tube's strength. In contrast to the structural body plies 26b, 26d, which are selected primarily for their strength, the innermost ply 26a and the outermost ply 26d may be selected primarily for other reasons. For example, it is common for a tube that is used as a core to be temporarily mounted onto a spindle which carries the tube and causes the tube to rotate, and the innermost ply 26a can be selected so that it will be compatible with the rotating spindle. Similarly, the outermost ply 26c can be selected so that it will be compatible with the product that is wound onto the tube.
FIG. 3 schematically illustrates a known process for applying an adhesive 38 to a ply 26 before the ply is spirally wound upon, and adhered to, the ply which was most recently previously wrapped around the mandrel 24. The ply 26 illustrated in FIG. 3 can be any one of the plies 26b-d illustrated in FIG. 1. As schematically illustrated in FIG. 3, the ply 26 is drawn past any type of conventional applicator 27 that applies the adhesive 38 onto the top surface of the ply 26. Then, the ply 26 is drawn past a stationary scraper 40, and the scraper arranges the adhesive and causes excess adhesive to flow off of the ply.
FIG. 4 is a schematic plan view of the scraper 40, and FIG. 6 is an enlarged view of a small portion of the scraper. The scraper 40 is in the form of a cylindrical rod with a series of closely spaced apart recesses 42 formed therein. Only a representative few of the recesses are identified by their reference numeral in FIG. 4. The recesses 42 are identical and are uniformly spaced apart from one another along the length of the rod 40. Each of the recesses 42 encircles the rod 40, and each of the recesses is uniform along its annular length.
FIG. 5 is a schematic top plan view of a portion of the ply 26 of FIG. 3 at a position immediately downstream from the scraper 40. FIG. 5 illustrates that the adhesive 38 (see FIG. 3) has been arranged in a series of longitudinally extending, uniformly and closely spaced parallel stripes 44. Only a few of the adhesive stripes 44 are identified by their reference numeral in FIG. 5. The arrangement of the adhesive stripes 44 on the ply 26 corresponds to the arrangement of the recesses 42 on the scraper 40, because the recesses 42 arrange the adhesive stripes 44. At most, preferably only a relatively thin layer of the adhesive is between adjacent adhesive stripes 44 on the ply 26 of FIG. 5, because the scraper 40 scrapes the adhesive away from these areas.
The recesses 42 and, thus, the adhesive stripes 44 are sized and uniformly closely arranged so that when the inner surface of the ply 26 is spirally wound upon, and adhered to, the ply which was most recently previously wrapped around the mandrel 24, the adhesive stripes 44 spread and merge with one another so that at least about 95% to 100% of the inner surface of the ply 26 is substantially adhered to the outer surface of the ply which was most recently previously wrapped around the mandrel. Thereafter, the ply 26 can be characterized as being “fully adhered” since at least about 95% to 100% of the inner surface of the ply 26 is substantially adhered to the outer surface of the ply which was most recently previously wrapped around the mandrel.
U.S. Pat. Nos. 6,230,968 and 6,409,078 disclose a composite can with a body wall that is spirally wound so that its edges form a butt joint. The can may be opened at the butt joint to access the product contained therein. An exterior label is spirally wrapped about and adhered to the outer surface of the body wall. In addition, a spirally wrapped liner is adhered to an inner surface of the body wall.
As one example, the '968 patent indicates that the adhesive that is between the label, which is also referred to as a cover layer, and the body wall is applied in a predetermined substantially continuous pattern between the inner surface of the cover layer and the outer surface of the body wall, with the pattern having a relatively higher-density screen pattern applied to a first region of the cover layer that overlies the butt joint of the body wall and a relatively lower-density screen pattern applied to a second region of the cover layer remote from the butt joint.
As another example, the '078 patent indicates that the adhesive is applied in a predetermined pattern between the inner surface of the cover layer and the outer surface of the body wall, with the pattern providing substantially less than 100% adhesive coverage of said surfaces. It is further indicated, among other things and according to this example, that the adhesive on the liner is applied in a predetermined pattern such that the adhesive covers substantially less than 100% of the liner.
The '968 and '078 patents indicate that it is conventional to apply adhesives to substantially the entire surface of strips that are spirally wound together to form composite cans. These patents further indicate, for example, that their inventions enable increased green strength and dimensional stability of composite cans so that parent tubes can undergo secondary operations with less susceptibility to being damaged, and so that the holding period for green cans may be reduced or eliminated. These patents also indicate, for example, that the invention, in preferred embodiments, enables enhanced performance of composite cans, such as improved burst strength of dough cans while still permitting intact label removal.
The '968 and '078 patents provide important improvements in the field of cans that are made of multi-ply tubes. However, further improvements that provide other balances of properties are desired, particularly for tubes that are used as cores for having products wound thereon. Tubes that are used as cores are subjected to different types of stresses than tubes that are used as cans, particularly cans that are to be opened at a ply's butt joint; therefore, a different balance of properties is desired for tubes that can be used as cores.